Porous concrete blocks are cast in molds and demolded after attaining their green strength. The still plastic (green) porous concrete block, which has a length of about 6 to 7.5 m, a width of about 2 m and height of about 65 to 75 cm, is taken to a cutting machine and cut there by means of tensioned steel wires in the longitudinal and transverse directions, so that rectilinear porous concrete bricks, blocks or even slabs result. These are then hardened under steam pressure in an autoclave. On cutting the still plastic porous concrete block, a layer about 3 to 12 cm thick is separated from the upper side and has to be removed before hardening. If the porous concrete block is cut lying horizontal, this waste layer is a layer of irregular height arising in blowing up the porous concrete mass. Porous concrete blocks are however according to DE-PS 958 639 also tipped over through 90.degree. after removal from the mold, so that they then stand on their long narrow side, and are cut precisely in this position. After the cutting the porous concrete block is then turned over through 90.degree. again on to its major wide side (cf. DE-PS 2 108 300), before placement in the autoclave. In cutting a block standing edgewise also, a waste layer of up to 12 cm thickness is taken off at the top, because the narrow side of the plastic porous concrete block can be contaminated by mold oil, the sidewall of the mold is not exactly flat or even runs mostly at a small angle to the wide side of the porous concrete block and because moreover, depending on the format of the bricks or slabs to be cut, there is a residue which is taken into account in the upper layer.
A known apparatus for removing the waste layer resulting in cutting the upper side of plastic porous concrete blocks or the like (DE-PS 1 683 837) comprises a suction box which can be lowered from above over the block and has a plurality of apertures in its underside. A cover arrangement in the form of a flexible film is provided beneath these apertures and can be drawn over a part of the apertures like a blind, in order to cover them. In this manner the apparatus can be used to lift off waste layers of different sizes. The known apparatus is however expensive to manufacture and operate. Since it operates with a vacuum and dust and porous concrete particles get into the suction air when sucking up the waste layer, filters for dust removal from this air are needed and regularly have to be cleaned. If the vacuum suddenly disappears because of loss of current or other disturbance to operation, the waste layer lifted off by the apparatus can moreover come away from the suction box and fall down on to the already cut porous concrete block located thereunder. This is already enough to damage the uppermost porous concrete bricks or slabs, which are then also waste, even with removal of the broken up waste layer by hand.
The object of the invention is to provide an apparatus for removing the waste layer arising in cutting porous concrete blocks, especially porous concrete blocks or the like standing on edge, which can be made inexpensively, involves small operating costs and also has a long working life.